The invention relates to molecules having ANT-ligands properties.
It more particularly relates to molecules useful for inducing apoptosis or similar cell death mechanisms and their use as therapeutical agents.
Since ten years ago, the mitochondrion has been progressively recognized as an integrator-coordinator of apoptosis and a major checkpoint leading, upon activation, irreversibly to a regulated cell death process, namely mitochondrial apoptosis. This process is favored by a sustained Ca2+ accumulation in the mitochondrial matrix and manifests as signs of pro-apoptotic mitochondrial alteration, namely permeability transition, dissipation of the electrochemical potential, matrix swelling, cristae remodelling, relocalization of Bax to mitochondria and the release of pro-apoptotic factors such as cytochrome c and AlF from mitochondria. Depending on the physiopathological models, mitochondrial membrane permeabilization (MMP) would affect the outer mitochondrial membrane or both membranes, i.e. the outer and the inner membrane. MMP is under the control of Bax and Bcl-2 family members, which are respectively pro- and anti-apoptotic. Thus, apoptosis can be inhibited by overexpression of oncogenes (e.g. Bcl-2) or viral proteins (e.g. Vmia from Herpes virus). MMP is usually accompanied by a bioenergetic catastrophe: a loss of transmembrane potential (L4m), an arrest of respiration, a decrease in ATP level and an increase in reactive oxygen species (ROS) levels. In this context, two constitutive mitochondrial proteins, the adenine nucleotide translocator (ANT, inner membrane (IM)) and the voltage-dependent anion channel (VDAC, outer membrane (OM)), cooperate with the Bax and Bcl-2 proteins family. Bax is a pro-apoptotic cytosolic protein, which interacts with ligands, such as Bid and PUMA, activates and translocates to the mitochondrion to induce cell death. Furthermore, the ANT-Bax cooperation has been reported in several physiopathological models. These proteins belong to the mitochondrial permeability transition pore (PTPC), a multiprotein complex localized at the contact sites of the OM and IM membranes. The precise composition of this pore is still unknown but, several independent hypotheses converge to the possibility that ANT (IM) and VDAC (OM) interact to form a double channel. In normal conditions, this double channel opens transiently and mediates the channelling of ATP from the matrix (site of synthesis) to the cytosol (final destination). Upon stimulation by a wide range of endogenous as well as exogenous stimuli, PTPC opens as a high conductance channel to allow the free passage of water and metabolites of MM<1.5 kDa, inducing a matrix swelling and the subsequent rupture of the OM, thus facilitating the release of mitochondrial proteins into the cytosol. This model has been challenged by a publication in 2004 based on the generation of conditional double-knock out mice for ANT1 and ANT2 in the liver, two isoforms of ANT, suggesting that ANT could be dispensable for apoptosis (1). Nevertheless, a novel ANT isoform (ANT4) has been identified recently (2,3) and, as ANT represents the most abundant member of a large family of highly homologous members, i.e. the mitochondrial carriers, in the absence of ANT, another carrier might replace the functional role of ANT for the induction of MMP to compensate the absence of ANT1 and 2 (4,5).
Interestingly, Jang et al. (6) demonstrated that ANT2 suppression by vector-based siRNA inhibits tumour growth in in vivo human breast cancer models. This reveals the therapeutic potential of an ANT targeting approach in oncology. An attempt to target pharmacologically ANT has been previously undertaken, using the peptidic approach (7,8), and preliminary results revealed several technological difficulties, resulting from the fact that peptides cannot penetrate into the cell and need to be coupled with targeting sequences (e.g. Tat, Ant).